1. Field of the Invention
The invention relates to an implant for surgical use in humans or vertebrates, in particular for the replacement, for the partial replacement or for the strengthening of a damaged intervertebral disk or for the replacement, for the partial replacement or for the strengthening of an anatomical joint.
2. Description of Related Art
The supporting structure of the human body, the skeleton, is composed of bone and cartilage. Together with tendons, ligaments and muscles, it forms the musculoskeletal system in humans and vertebrates.
Here, the joints serve as connection sites between the bones and are responsible for the mobility of the body. In addition to guaranteeing mobility, the joints here especially additionally perform the absorption or compensation of the pressure on the skeletal system which results on standing and jumping. The inter-vertebral disk which lies between each two adjacent vertebrae in man and vertebrates also has this task.
For example, in humans alone the vertebral joints and the joints in the hip and knee are stressed just by standing upright and walking. As a result of wear processes, caused, inter alia, by age, disease or overstressing, wear of the joints or vertebrae or the joint surfaces results. Under certain circumstances, this leads to restricted mobility, decrease in strength or pain. This can be compensated, however, by a replacement, a partial replacement or a strengthening of the joints by means of an implant.
Here, the implant should essentially correspond to the dimensions and the shape of the joint to be replaced or of the intervertebral disk to be replaced, have adequate biocompatibility with the surrounding tissue and especially comparable physical properties, in particular with respect to rigidity, elasticity, resilience and damping, and make possible unrestricted movement within the course of natural movement and have a long lifetime in order not to stress a patient by frequent implant changes.
To this end, a multiplicity of different implants have been provided. For example, in the case of a joint, such as a shoulder, hip or knee joint, the joint capsule or condyle and socket are exchanged with plastic implants, which must be firmly anchored in the bone. In this connection, a distinction is made between the total endoprosthesis, in which both the condyle and socket are replaced, and the partial endoprosthesis in which only the condyle is replaced.
Further known materials or material combinations for forming the joint coupling, i.e. for forming the socket and condyle or for forming the surfaces of the socket and condyle rubbing on one another, include the coupling of metal/metal, plastic/metal, plastic/ceramic or ceramic/ceramic. In the selection of the material combination, in addition to the biocompatibility, the long-term anchoring of the implant in the body, the wear and the abrasion on the joint surfaces of the artificial joint play a crucial role. Here, the abrasion depends on the materials of the joint coupling. Plastics disadvantageously exhibit increased wear on account of increased abrasion compared with metal surfaces or ceramic surfaces which are precisely ground with respect to one another.
The structures of the bones or of the joints are adjusted in their function, especially with respect to rigidity, elasticity, resilience and damping, such that they optimally conform to the local stress. This functionally adjusted structure is disturbed by the incorporation of an implant on account of changed extension behavior and changed force transmission by the implant, especially in the case of metals or ceramics, in the bones. The force transmission of the implant in the bones in this case plays a crucial role in the question of the long-term anchoring or fixing of the implant in the body.
Moreover, in order to guarantee solid growing together of the implant with the bone by bone ingrowth into the implant, the outsides of the implants oriented toward the bone are provided with a surface structuring.
For the replacement of intervertebral disks, the specification DE 696 23 535 T2, for example, discloses an artificial intervertebral disk which has a two-part, hard, chromium-coated metallic ball joint bearing system and makes possible unrestricted movement, but at the same time is unable to absorb shocks to the spinal column. Moreover, the surfaces of the ball joint bearing system moving on or against one another must be precisely and therefore expensively processed in order to avoid or to minimize accelerated wear of the surfaces caused, inter alia, by friction.
The document DE 694 28 143 T2 discloses, for the replacement of a damaged intervertebral disk, an intervertebral disk prosthesis which comprises an upper rigid plate, a lower rigid plate and an elastomeric core, which is arranged between the plates and adjoins these. Owing to its elastomeric core, this implant exhibits shock absorption and, together with low rigidity, adequate mobility. However, the elastomeric core can be degraded by the body over time. Moreover, elastomers tend to deform over time and thereby to change their dimensions and properties.
Both implants have projections on the outsides oriented in the direction of the vertebrae in order to fix the implant into the vertebrae. Moreover, in both implants said outsides are additionally provided with a porous coating in order to make possible an ingrowth of tissue or bone ingrowth into the implant by the surrounding vertebrae and thereby to connect the bone more strongly with the implant.